This invention relates generally to gas-insulated equipment, and more particularly to a gas-filled bushing utilizing a self-adjusting bushing flange seal.
Gas-insulated equipment is being used in an ever increasing scale in recent years due to the desirablility of increasing safety, problems in acquiring the necessary acreage for substations and right-of-way for overhead lines, higher power requirements of growing metropolitan areas, and the overall growing demands for electrical energy. Typical of such installation are gas-insulated, high-voltage substations dealing with voltages of magnitudes such as 500,000 volts and higher with main components such as circuit breakers, switches, and the like enclosed in gas-filled grounded metal containers which are interconnected by elongated conductors which also are contained in outer grounded sheaths filled with the insulating gas. Typical of the gas utilized in these substations is sulfur hexafluoride whose high dielectric strength minimizes the separation distance required between adjacent electrical components, to thereby decrease the size of the equipment.
Generally, whenever utilizing gas-insulated equipment, it is necessary to provide an air entrance bushing to make the connection from an overhead line, for example, to the central gas-insulated conductor of the gas-insulated bus. Presently, these bushings generally consist of an elongated porcelain or epoxy body of tapering or straight diameter with suitable corona rings at the ends of the body to allow adequate flaring of dielectric potential lines.
Because these bushings are of porcelain or epoxy material, welding or brazing of these bushing shells to interconnect them with the gas-insulated system is inapplicable or difficult. However, the securing of these bodies to the remainder of the system requires a gas-tight seal, for otherwise the gas disposed within the bushing or within the system could escape through such connection thereby decreasing the dielectric strength of the system. A prior practice has been to utilize seals disposed between the bushing shell and the flange to which it is secured by cement to prevent the escape of the insulating gas. However, problems have arisen with the use of such seals. Both the flange weldment and the bushing shell require very flat and accurate surfaces at the location of the seal to prevent the escape of the insulating gas, which is difficult to achieve. One method of compensating for this is to force the seals into greater compression between the bushing shell and the flange; however, care must be asserted when compressing this seal, for too much pressure may cause the porcelain or epoxy bushing shell to crack. Therefore, what is desirable is to provide a means for controlling the compression force of the seals against the bushing shell without increasing the probability of cracking the shell or shearing the flange off, and without requiring close and expensive dimensional tolerances of all components.